Embed Size (px)
Citation preview
Work and EnergyDefinition of Work
Kinetic EnergyPotential Energy
Conservation of Mechanical EnergyPower
Efficiency
What is work?
The product of Force and distance moved
In the direction of the force
In the direction of the force
Force and displacement must be in the same dimension
Parallel or antiparallelIf parallel, work done is positive
If antiparallel, work done is negativeIf force is perpendicular to
displacement, work done is zero.
Negative work is also referred to asWork done against the antiparallel force
F
sPositive workWork = F x s
Units for Work: Nm or Joule, J
Normal Force
Friction
Tension
Weight
• Work done by• Weight
• Zero• Normal
• Zero• Friction
•Negative
Work = (F cos 30) x s
s
No work forGravity andNormal force
Examples
How do you calculate for total work?
To calculate for total work
Sum of all of the work done by each forceOr
Net force x displacement
Points on Total Work
If net force is zero, total work is also zero.If net work is not zero, then the body is
accelerating.Equation
What is energy?
The stored ability to do work
Kinetic Energy of an object
Stored ability to do work because of its motion.
Work –Energy Theorem
Examples
The work done by gravity
Second case
(Gravitational) Potential Energy of an object
Stored ability to do work as a result of it position.
Conservation of Mechanical Energy
Examples
Power
The rate of doing workWork done per unit time
EquationUnits
Power and Quality of work are not the same.
Efficiency
Power output per power input
ExampleA simple pendulum, consisting of a mass m, is attached to the end of a 1.5 m length of string. If the mass is held out horizontally, which makes a 60°angle with the vertical, and then released from rest, what is its speed at the bottom?
Example
If the 1000- kg roller coaster leaves Point Q from rest, how fast is it traveling at Point R?
Example
If the 1000-kg roller coaster leaves Point Q from rest, what is its speed at Point S?
Past Paper Example
Past Paper Example
Past Paper Example
